Apparatus for processing and vitrifying waste

ABSTRACT

The invention relates to apparatus for processing waste, in particular hospital waste, the apparatus including a gasification chamber (1) into which the waste is inserted to be subjected to degassing and to combustion, a post-combustion chamber (2) for the gases coming from the gasification chamber, and a melting chamber (3) in which the slag coming from the gasification chamber (1) is exposed to high temperature for vitrification purposes.

BACKGROUND OF THE INVENTION

The present invention relates to apparatus for processing waste, andintended more particularly but not exclusively for processing hospitalwaste.

In general, hospital waste comprises a wide variety of solid and liquidmaterials (glasswork, needles, scalpels, chemical substances, biologicaltissue, . . . ) that may be biologically contaminated or toxic and whichmust be handled with special precautions, and in particular the wastemust be double-wrapped. Hospital waste packaged in this way constitutesbatches containing large fractions of volatile substances and having arelatively high lower calorific value (LCV) of 14,600 kJ/kg. Thiscalorific value is nevertheless highly variable and may reach extremevalues of 4,200 kJ/kg and 29,000 kJ/kg. In addition, the processing ofhospital waste is subject to regulations that require batches of wasteto be stored for no more than a short period on the incineration site,and for hygiene reasons, the waste cannot be removed from its packagingprior to incineration in order to make up batches of uniform calorificvalue. Thus, when incinerating hospital waste, it is necessary toprocess a succession of batches in which the calorific value varies in amanner that is not known accurately since, in practice, it is notpossible for the personnel in charge of incinerating waste to obtaindetailed information about the contents of each batch.

SUMMARY OF THE INVENTION

Incinerators are known for destroying household waste in which waste isburned in a hearth fitted with a grid on which the waste is depositedand into which air is injected in order to activate combustion. Suchknown incinerators are poorly adapted to destroying hospital waste,firstly because of the risk of biologically contaminated liquids runningout through the grid or of substances melting that might clog the grid,and secondly because the maximum temperatures reached in suchincinerators are less than the temperatures at which steel melts, and asa result metal objects contained in the waste, e.g. needles andscalpels, remain identifiable after processing.

Patent FR 1 394 418 proposes a processing apparatus that includes agasification chamber in which the waste is inserted so as to besubjected therein to degassing and to combustion, a chamber forpost-combustion of the gases coming from the gasification chamber, and amelting chamber in which the slag from the gasification chamber ismelted for vitrification purposes. In that apparatus, the gasificationchamber includes a grid beneath which oxidizing agents are directed at arate which is adjusted so that the organic components of the waste areburned completely prior to the waste being delivered to the meltingchamber. Oxidizing agents and fuel are blown into the melting chamber soas to provide flames therein of greater or lesser reducing activity forthe purpose, where necessary, of reducing metal oxides and of recoveringmetal. That known apparatus makes it possible to use waste to produceresidues that are usable in the form of granules or of molded parts.Nevertheless, it consumes large quantities of oxidizing agents and ofenergy for the purpose of burning the waste completely prior to applyingit to the melting chamber and reducing the metal oxides. In addition,the use of oxidizing agents in considerable excess gives rise to anequivalent increase in the flow of gases leaving the apparatus and anequivalent increase in the cost of processing said gases forde-pollution purposes.

An object of the present invention is to provide apparatus forprocessing waste, in particular hospital waste, that enables combustionof the waste to be controlled thoroughly and that also enables it to betransformed into an inert vitrified solid residue that can be made useof subsequently, while avoiding excessive energy consumption andunacceptable overall cost for the installation.

The present invention achieves this object by means of an apparatus ofprocessing waste, in particular hospital waste, the apparatus comprisinga gasification chamber into which the waste is inserted in order to besubjected to degassing and to combustion, a post-combustion chamber forthe gases coming from the gasification chamber, and a melting chamber inwhich the slag coming from the gasification chamber is subjected to hightemperature for vitrification purposes, means for injecting air into thegasification chamber and into the gas post-combustion chamber, thegasification chamber being above the melting chamber so that the slagmoves down into it under gravity to be subjected to melting, theapparatus being characterized in that it includes means for regulatingthe flow rate of air injected into the gasification chamber so that itmatches the calorific value of the waste being processed and so that thecontent of unburned matter in the slag inserted into the melting chamberlies in the range 3% to 10%.

Unlike known apparatuses, this achieves controlled and incompletecombustion of the waste in the gasification chamber, thereby making itpossible, compared with known apparatuses, to reduce both energyconsumption and the quantity of air that is injected. It is neverthelesspossible to recover vitrified products in which the content of unburnedsubstances is low. In particular, an unburned content of less than 0.1%is achieved when the temperature that obtains in the melting chamber isadvantageously about 1600° C. and is preferably obtained by means of aplasma torch. By appropriate regulation of the air flow rate, it ispossible to feed the gasification chamber at the beginning of wastecombustion with less than enough air, thereby preventing the mostcombustible and the most volatile components thereof (plastics,alcohols, . . . ) bursting into flame and burning in a manner that wouldgive rise to combustion running away in uncontrollable manner.Thereafter, once the volatile components have been eliminated,combustion can be activated by increasing the air flow rate. The airflow rate thus remains matched to the calorific value of the waste beingprocessed and thus makes it possible to avoid gas appearing in unwantedgusts. By likewise regulating the rate at which air is injected into thepost-combustion chamber, it is possible to obtain a substantiallyconstant total flow rate of gas leaving the apparatus and going toprocessing and/or heat recovery installations. Finally, any excessenergy consumption is avoided and the cost of downstream gas processinginstallations is reduced.

Other characteristics and advantages of the present invention appear onreading the following description of a non-limiting embodiment of theinvention and on examining the accompanying drawing which is afragmentary diagram of processing apparatus of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a planar side view portion of the processing apparatusof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The processing apparatus comprises a gasification chamber 1 into whichwaste is injected in order to be subjected therein to gasification andto combustion, a post-combustion chamber 2 for post-combustion of thegases coming the gasification chamber 1, and a melting chamber 3 wherethe slag coming from the gasification chamber 1 is exposed to hightemperature for vitrification purposes.

More particularly, waste is inserted into the gasification chamber 1along arrow D by means of a loader device 10 making it possible toreload the gasification chamber 1 regularly and frequently (e.g. aboutten times per hour) without allowing unwanted air to penetrate therein,the device comprising a hopper 11 provided with a closure lid 12. Thehopper 11 leads to an intake air-lock 13 fitted with a door 14 givingaccess to the gasification chamber 1. A pusher 15 driven by an actuatormechanism 16 is adapted to push waste deposited in the airlock 13 intothe gasification chamber 1 when the door 14 is open and the lid 12 isclosed. The door 14 is preferably mounted to slide vertically and it isactuated by an actuator. As an indication, in the embodiment described,it is associated with a rectangular opening to the gasification chamber1 having the following dimensions: 1.5 meters (m) ×1.6 m.

The gasification chamber 1 is generally elongate in shape along ahorizontal axis and it has a cross-section that is rectangular. The door14 opens out in an end face of the gasification chamber 1 that isreferred to as the "front" face, and that is situated to the right ofthe drawing. By way of indication, the length of the gasificationchamber 1 may be 9 m in the example described and its inside volume maybe 57 m³, thereby enabling waste to be processed at a rate of about 2metric tons per hour (t/h). The inside of the gasification chamber 1 islined with refractory material in conventional manner. By way ofindication, in the example described, the wall 4 of the gasificationchamber 1 is constituted by 10 mm thick steel sheet lined on the insidewith a thickness of 22 cm of refractory materials. The bottom insidesurface of the gasification chamber 1 includes refractory soleplatesorganized as a staircase, and more particularly in the exampledescribed, the gasification chamber 1 includes a first soleplate 21close to the door 14, followed by second and third soleplates 22 and 23in a configuration going downwards in steps from the first soleplate 21and away from the door 14. In the embodiment described, the soleplatesare slabs having a side of about 2.5 m. Naturally, depending on thequantity of waste to be processed, it is possible to lengthen or shortenthe gasification chamber 1, with the number of soleplates being modifiedaccordingly so as to determine the transit time of the waste. As shown,it is preferable for the bottom of the airlock 13 for loading waste tobe situated at the same height as or at a height that is slightly higherthan the first soleplate 21 so that during loading newly inserted wastepushes against waste that is already burning on the first soleplate 21without covering it completely and thus without damping the fire. Thewaste on the first soleplate 21 is subjected to degassing and the lowboiling point materials and liquids contained in the waste evaporate. Aprimary burner, known per se and not shown, is placed in the vicinity ofthe first soleplate 21 to cause the first fill to burst into flame andit generally operates only during the first few minutes after theapparatus is put into operation. The end of the gasification chamber 1remote from the door 14 is fitted with a burner 5 for the purpose, wherenecessary, of maintaining combustion in the gasification chamber 1 sothat the temperature therein remains within the range 600° C. to 900° C.The end of the gasification chamber 1 is fitted with a door (not shown)used for maintenance of the processing apparatus.

Combustion air is delivered into the gasification chamber 1 via lateralopenings 70 distributed along the length thereof level with itssoleplates. The combustion air is delivered by a conventional fan (notshown) and regulator means are provided to act, in particular, on therate at which air is injected into the gasification chamber 1 in amanner described below, which air is also referred to as primary air.

The gasification chamber 1 is provided with water sprayers for thepurpose of cooling the chamber in the event of its inside temperaturebecoming too high, e.g. greater than 1000° C.

When the waste reaches the rear end of the first soleplate 21, i.e. theend that is situated to the left in the drawing, it drops onto thesoleplate 22 which is situated further down, and subsequently onto thethird soleplate 23. By dropping onto a lower soleplate, the waste findsitself dispersed and stirred, thereby enhancing aeration and combustion.

Pushers of refractory material and known per se (not shown and sometimesknown as "pokers"), are actuated periodically by actuators (e.g. every 3minutes to 10 minutes depending on the processing capacity of theinstallation), and they are mounted between the soleplates on the axisof the gasification chamber 1 to push the waste horizontally away fromthe door 14, i.e. towards the end of the gasification chamber 1 that issituated to the left in the drawing. These pushers also serve to cleanthe soleplates, in which case they are extended to the maximum.

The gasification chamber 1 overlies the melting chamber 3 and the slagthat results from combustion of the waste in the gasification chamber 1leaves the last soleplate, i.e. the third soleplate 23 in the embodimentdescribed, via a vertical passage or well 30 so as to fall into themelting chamber 3 where they are subjected to the action of a plasmatorch 50 that is known per se.

The gases coming mainly from degassing of the waste in the gasificationchamber 1 (and to a smaller extent from the melting chamber 3) leave thegasification chamber 1 upwardly via a passage 40 which is situated inthe example described substantially over the third soleplate 23 andwhich leads to a gas post combustion chamber 2. The end wall of thegasification chamber 1 connecting the well 30 to the passage 40 slopesupwards and forwards, i.e. to the right in the drawing. Thepost-combustion chamber 2 is elongate in shape along a horizontal axisand the gases are preferably admitted eccentrically relative to saidaxis so as to impart helical motion to them within the chamber 2. Thepost-combustion chamber 2 overlies the gasification chamber 1 and itincludes lateral opening 75 for admitting combustion air referred to as"secondary air". This air is injected into the combustion chamber 2 in adirection that is likewise selected to impart generally helical motionto the gas, thereby enhancing intimate mixing of the secondary air withthe gas coming from the gasification chamber 1. The post-combustionchamber 2 is fitted with a secondary burner 41 actuated, if necessary,to keep the temperature in said chamber above 850° C., and preferably inthe range 850° C. to 1200° C. The hot and fully-burned combustion gasesleave the post-combustion chamber 2 in the direction of arrow G and aresucked by a fan 60 whose suction rate is controlled so as to maintain asmall amount of suction in the post-combustion chamber 2 and in thegasification chamber 1. The burned gases sucked by the fan are appliedto a heat recovery boiler and/or to physical or chemical treatment forthe gases, for the purpose of eliminating toxic compounds (chlorine,heavy metals, dust, . . . ) contained therein.

The primary air and the secondary air are preferably produced by meansof a single fan fitted with distributor flaps enabling the distributionof air delivered to the gasification chamber 1 and to the gaspost-combustion chamber 2 to be adjusted while maintaining a total flowrate of air injected into the two chambers which is matched to thecalorific value of the waste being processed.

In the example described, the melting chamber 3 is in the form of acrucible (also referred to as a ladle) lined with refractory material,which is generally cylindrical about a vertical axis, and which isfitted with the other-mentioned plasma torch 50 or with any otherequivalent device known to the person skilled in the art (electric arc,electrical burner, oxygen burner, . . . ). The melting chamber 3 isfitted with an additional burner 55 for providing initial heating andfor preventing excessive cooling of the melting chamber when the torch50 is not operating. The burner is retractable and it is retracted whenthe torch is in operation.

The temperature that obtains inside the melting chamber 3 is monitoredby optical pyrometry and it is maintained at a reference value(preferably 1600° C.) by modulating the power of the torch 50.

Under the action of the heat generated by the plasma torch 50, the slagpoured into the melting chamber 3 melts and forms a melt. An orifice 51is provided at the bottom of the melt 3 to enable the melt to beevacuated in the direction of arrow L towards a tank 52 that is filledwith water and that forms a quenching tank in which the poured melt issubjected to sudden cooling causing it to fragment and formvitrification products. Naturally, without going beyond the ambit of therepresent invention, it is possible to propose cooling the melt 3 by anyother means known to the person skilled in the art, e.g. by air cooling.

The orifice 51 is fitted with a conventional shutter that is actuated byan actuator (not shown) controlled to cause the melt to be pouredcyclically into the quenching tank. In a variant, the orifice 51 may beleft open and it may be situated at a height relative to the bottom ofthe crucible such that the melt is evacuated continuously byoverflowing.

The dimensions of the melting chamber are determined relative to thevolume of slag poured therein, given that the slag constitutes about 10%to 15% of the incoming volume of waste.

Vitrification products are extracted from the quenching tank 52 by anyappropriate means known to the person skilled in the art, e.g. by meansof a bucket conveyor 54.

The processor device of the invention operates as follows.

The lid 12 of the hopper 11 is opened and hospital waste packaged incontainers of combustible material is dropped into the airlock 13. Thelid 12 is closed, the door 14 is opened, and the actuator mechanism 16is actuated to drive the pusher 15 towards the door 14, therebyexpelling the waste contained in the airlock 13 into the gasificationchamber 1. Thereafter the pusher 15 is withdrawn, the door 14 closed,and a waste incineration cycle begins.

The cycle begins with a degassing stage which takes place on the firstsoleplate 21 and during which less than enough combustion air isdelivered into the gasification chamber 1 so as to ensure that the mosthighly combustible and the most volatile components (plastics, alcohols,. . . ) do not burst into flame, since if they were to burn too quicklythat would give rise to uncontrolled combustion runaway. The temperaturethat obtains inside the gasification chamber lies in the range 600° C.to 900° C. The flow rate of primary air preferably corresponds to about30% of the total air flow rate and the flow rate of secondary aircorresponds to about 70%. After a few minutes, the volatile componentsare eliminated and combustion is activated by increasing the flow rateof primary air, by acting on the above-mentioned flaps, so as to giverise to normal combustion. The flow rate of primary air then preferablyreaches 50% of the total air flow rate but it continues to be regulatedas a function of temperature and as a function of the suction measuredin the gasification chamber 1 and at the outlet from the gaspost-combustion chamber 2. The secondary air flow rate iscorrespondingly reduced to 50%. In the event of combustion beginning torun away, the regulation means detect a rapid increase in pressure inthe gasification chamber 1 and reduce the rate at which primary air isinjected into the gasification chamber. Water sprayers are automaticallybrought into operation if the temperature or the pressure reach valuesthat are excessive. These various regulation actions make it possible tocontrol degassing and combustion and to avoid any unwanted gusts of gasappearing, such that the flow rate of gas leaving the apparatus towardsinstallations for further processing and/or heat recovery remainssubstantially constant.

The combustion waste situated on the first soleplate 21 is pushed awayfrom the odor 14 when the next charge is inserted, thereby falling ontothe second soleplate 22. The flow of air injected to the secondsoleplate 22 and to the following soleplate 23 is regulated in such amanner as to ensure substantially complete combustion of organic wastethereon. Periodically, the refractory pushers situated between thesoleplates are actuated to move the waste towards the far end of thegasification chamber 1. The waste pushed in this way from soleplate tosoleplate is transformed into slag and it finally drops into the meltingchamber 3 via the well 30. The temperature of the slag entering themelting chamber is preferably greater than 800° C. To avoid dust beingentrained by the gas leaving the melting chamber 3, the torch 50 ispreferably switched off while the pusher on the last soleplate isadvancing and causing slag to fall. The slag falls into the melt and itbegins itself to melt, and the torch is then put back into operation tocomplete melting. Periodically, the shutter fitted to the orifice 51 isactuated and the melt pours out from the melt chamber 3 so as to fallinto the quenching tank 52 where it solidifies and fragments. Thevitrification products are removed from the quenching tank 52 by theconveyor 54.

During combustion and degassing of the waste in the gasification chamber1, the gas coming therefrom and also the gas coming from the meltingchamber 3 is sucked by the fan 60 into the gas post-combustion chamber 2which is maintained at high temperature (850° C. to 1200° C.),optionally by means of an additional burner 41. At the inlet to the gaspost-combustion chamber 2, the gas receives an injection of secondaryair causing it to be fully oxidized. The flow rate of secondary airinjected into the chamber 2 is continuously regulated by the regulationmeans which measure the residual oxygen and carbon monoxide content ofthe gases leaving the chamber 2. The transit time of the gas through thechamber 2 is greater than 2 seconds. The high degree of turbulence thatobtains inside the gas post-combustion chamber 2 serves to destroyparticles of soot and carbon monoxide, and to dissociate hydrocarbonsand chlorine-containing compounds.

The high temperature that obtains in the melting chamber 3 ensurescombustion of substantially all of the unburned matter contained in theslag poured into said chamber, thereby making it possible to accept slaghaving an unburned content lying in the range 3% to 10%, and thus makingit possible to accept a relatively short transit time for the wastethrough the gasification chamber 1 (about 30 minutes), with a highloading of waste per unit area therein (150 kg/m²).

The combined action of the gasification chamber 1 and of the meltingchamber 3 makes it possible to obtain an unburned matter content of lessthan 0.1% in the vitrification products while consuming less energy thanwould be necessary to obtain the same content of unburned matter using asingle gasification chamber 1 (in which the waste would need a longertransit time) or by means of a single (large volume) melting chamber inwhich the waste would be subjected directly to the action of a (morepowerful) plasma torch. The nitrogen oxide content of the gas leavingthe apparatus increases with the power of torch used, and said contentis reduced in the invention relative to that which would arise fromdirect vitrification of waste in a large-sized melting chamber fittedwith a torch of greater power. In practice, unburned matter is presentin trace form in the vitrification products.

In addition, the relatively high content of unburned matter that isacceptable at the outlet from the gasification chamber 1 makes itpossible to reduce the excess quantity of air injected into said chamberto about 80% of the value theoretically required for achievingcombustion of the waste with less than 3% of residual unburned matterinstead of the value of 150% which is generally used in knownincinerators. The total flow rate of gas leaving the processor apparatusis thus smaller than that leaving known installations, and consequentlyit is advantageously possible to make use of installations for treatingsaid gases and/or recovering heat therefrom that are smaller in size andthat present higher performance for equivalent cost.

Finally, the processor apparatus of the invention makes it possible todestroy hospital waste by transforming it into inert vitrificationproducts and it also makes it possible, in particular, because of goodcontrol of combustion in the gasification chamber and the low torchpower used, to ensure that no unburned matter is present (soot,hydrocarbons, carbon monoxide, . . . ) in the gas leaving the apparatus.In addition, waste is destroyed with improved energy efficiency giventhe low power of the torch used and the relatively high level ofunburned matter that can be accepted in the slag.

Naturally, the apparatus of the invention is applicable to processingwaste other than hospital waste.

The present invention is not limited to the embodiment described. Thus,for example, without going beyond the ambit of the invention, it ispossible to propose replacing the gasification chamber 1 having astaircase of soleplates with a gasification chamber of some other typethat enables degassing to be performed and that provides good control ofcombustion, e.g. a downwardly sloping rotary gasification chamber.

We claim:
 1. Apparatus of processing waste, in particular hospitalwaste, the apparatus comprising a gasification chamber into which thewaste is inserted in order to be subjected to degassing and tocombustion, a post-combustion chamber for the gases coming from thegasification chamber, and a melting chamber in which the slag comingfrom the gasification chamber is subjected to high temperature forvitrification purposes, means for injecting air into the gasificationchamber and into the gas post-combustion chamber, the gasificationchamber being above the melting chamber so that the slag moves down intoit under gravity to be subjected to melting, the apparatus beingcharacterized in that it includes means for measuring the temperatureand the pressure in the gasification chamber and for regulating the flowrate of air injected into the gasification chamber as a function of themeasured temperature and pressure so that the flow rate matches thecalorific value of the waste being processed and so that the content ofunburned matter in the slag inserted into the melting chamber lies inthe range 3% to 10%.
 2. Waste processing apparatus of claim 1, whereinthe flow rate of air injected into the gasification chamber and the flowrate of air injected into the post-combustion chamber are regulated sothat the flow rate of air leaving the apparatus for feeding toinstallations for processing gas and/or recovering heat is substantiallyconstant.
 3. Waste processing apparatus of claim 1 or 2, wherein thegasification chamber is constituted by a downwardly sloping rotarychamber.
 4. Waste processing apparatus of claim 1 or 2, wherein thegasification chamber includes soleplates on its bottom inside surfacethat are disposed in a staircase configuration and on which waste spendstime in succession, the soleplates being fitted with waste advancingpushers.
 5. Waste processing apparatus of claims 1 or 2, wherein thechamber of the melting chamber is maintained at a reference value. 6.Waste processing apparatus of claims 1 or 2, wherein the melting chamberincludes an orifice fitted with a shutter for enabling the melt to bedischarged to a quenching tank.
 7. Waste processing apparatus of claims1 or 2, wherein the temperature of the gas post-combustion chamber liesin the range 850° C. to 1200° C.
 8. Waste processing apparatus of claims1 or 2, wherein the air injected into the gasification chamber and intothe gas post-combustion chamber is obtained from a single fan.
 9. Wasteprocessing apparatus of claims 1 or 2, wherein the flow rate of primaryair injected into the gasification chamber lies in the range 30% to 50%of the total injected air flow rate, and the flow rate of secondary airinjected into the post-combustion chamber lies in the range 50% to 70%of the total injected air flow rate, the secondary air flow rate beingat a maximum at the beginning of waste processing and the primary airflow rate being at a maximum at the end of waste degassing.
 10. Wasteprocessing apparatus of claims 1 or 2, wherein the total injected airflow rate corresponds to air being 80% in excess over the theoreticalquantity required for ensuring combustion of the waste, with less than3% of residual unburned matter.
 11. Waste processing apparatus of claims1 or 2, wherein the unburned matter content of the vitrificationproducts is less than 0.1%.
 12. Waste processing apparatus of claims 1or 2, wherein the temperature of the slag on being inserted into themelting chamber is greater than 800° C.